FIG. 15 shows an antitheft system conventionally used in stores wherein commodities such as compact disk cassettes and magnetic tape cassettes are on display for sale, to protect these articles from shoplifting or like illegal acts.
The antitheft system comprises an antitheft gate 4 installed in the vicinity of an exit 40 of the store, and an alarm unit 3 attached to a commodity 5. The antitheft gate 4 has a circuit board 41 and a transmitting antenna (not shown). The circuit board 41 is provided with a transmitting circuit (not shown) for producing an alarm activating signal for the alarm unit 3.
With reference to FIG. 16, the alarm unit 3 comprises a buzzer 31, circuit board 33, battery (not shown), etc. which are housed in a casing 30. The casing 30 has a surface formed with sound emitting holes 34 and an alarm actuating switch piece 32. The buzzer 31 has its operation controlled by the circuit board 33 and is adapted to produce an alarm when the unit 3 is removed from the commodity or when the unit 3 passes by the antitheft gate 4.
The commodity is placed on display in the store, with the alarm unit 3 attached thereto. When selling the commodity to the customer, the clerk holds the buzzer 31 out of operation by sending a specified signal from a nullification device (not shown) to the circuit board 33 of the alarm unit 3, then removes the unit 3 from the commodity and hands the commodity to the customer in exchange for money.
If the customer wrongfully removes the alarm unit 3 from the commodity 5, the switch piece 32 is turned off to actuate the buzzer 31. Further if the customer acts to unlawfully bring the commodity 5 out of the store along with the alarm unit 3, the circuit board 33 of the alarm unit 3 receives an alarm activating signal from the transmitting antenna of the antitheft gate 4 to turn on the buzzer 31.
However, the antitheft system described has the following problem. It is likely that a customer or clerk temporarily employed will steal the nullification device from the store. The person stealing the nullification device can use the device unlawfully in other store to bring an alarm unit 3 out of alarming operation and then remove the alarm unit 3 from the commodity attached thereto, so that the commodity can be readily brought out of the store.